The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Time for human Hendra trial: scientist

The scientist who developed the Hendra vaccine wants to see it trialled on humans.

Almost a year after the Equivac vaccine became commercially available for horse inoculation, Professor Christopher Broder is hoping to secure funding to start human trials.

The US scientist says the Hendra virus protein, in every vaccine dose, has already been successfully tested on cats, ferrets, monkeys and horses.

The first foals recently born to horses vaccinated against Hendra also showed no complications, and Prof Broder says there's no reason why human trials can't go ahead.

"I'd certainly like to see that done," Prof Broder told AAP.

"We picked the right protein and we've been able to show in not only one animal model - but now four animal models - that there are no adverse reactions to the vaccination."

However, Prof Broder said he wasn't sure how soon he could secure funding for a phase-one safety trial.

"Whether or not those funds will become available in the next few years is anyone's guess considering the current state of research support in both the United States and Australia," he said.

Prof Broder said current testing focused on how often a horse's immunity against Hendra should be boosted.

Horses are believed to contract the virus from feed contaminated by urine, saliva or birthing fluids from flying foxes.

There's no known cure for Hendra, but the Equivac HeV vaccine aims to break the cycle of transmission and prevent human deaths.

Four people have died from the virus in Australia since 1994.

Even if the Hendra vaccine can't be tested on humans, Prof Broder is confident it will go a long way towards preventing Hendra virus in horses and people.

Every person infected with Hendra has contracted the virus from a horse, he said.

"The vaccine is going to break that chain of potential transmission and, in reality, if 90 per cent of horses end up getting vaccinated and it's taken up very well then Hendra virus is definitely not going to be a problem any more.

"And I think it has a really good chance of being that way."

Prof Broder will spend the next two weeks in Australia discussing the progress of the vaccine with government representatives and those who have been instrumental in fighting the Hendra virus.